The dental restoration of a partially or wholly edentulous patient with artificial dentition is typically done in two stages. In the first stage, an incision is made through the gingiva to expose the underlying bone. After a series of drill bits creates an osteotomy in the bone, a dental implant is placed in the jawbone for integration. The dental implant generally includes a threaded bore to receive a retaining screw holding mating components therein. During the first stage, the gum tissue overlying the implant is sutured and heals as the osseointegration process continues.
Once the osseointegration process is complete, the second stage is initiated. Here, the gum tissue is re-opened to expose the end of the dental implant. A healing component or healing abutment is fastened to the exposed end of the dental implant to allow the gum tissue to heal therearound. Preferably, the gum tissue heals such that the aperture that remains generally approximates the size and contour of the aperture that existed around the natural tooth that is being replaced. To accomplish this, the healing abutment attached to the exposed end of the dental implant preferably has the same general contour as the gingival portion of the natural tooth being replaced.
Once the clinician believes the implant is suitable for receiving a prosthesis, surgical techniques are used to place the dental prostheses by means of an abutment. According to one prior art abutment, the abutment is made from a ceramic material and has an internal bore through which a screw is inserted to hold the abutment on the implant. The internal bore of the ceramic abutment can be very abrasive. While installing the abutment using the screw, the internal bore can scratch and/or deform a seating surface on the head of the screw, which can negatively effect the connection between the abutment and the implant.
The screw may be pretensioned to prevent or minimize the separation between the individual components of a dental implant system, such as, for example, between the abutment and the implant. As a screw is fully threaded into a prethreaded bore in the implant, the screw is tensioned between the engaging threaded surfaces of the screw and the prethreaded bore, and the abutting surfaces of the screw head and a stationary seating surface around the bore in the implant. After the screw head seats on the stationary seating surface, the tension on the screw increases as the screw is threaded farther into the prethreaded bore. This tension on the screw produces a force that is commonly referred to as the “preload” of the screw. Thus, “preload” may be defined as the maximum initial force required to reverse out a tightened screw. Preload may also be described as the clamping force. By reducing the friction between the rotating surfaces of the screw and the opposed stationary surfaces, the preload on the screw can be increased for any applied torque because that torque will cause the screw to be advanced farther into its bore.